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8

The numbers you need are flow rates and desired temperatures. For example, Home Depot's guide gives the following flow rates: Bathroom Faucet: 0.5 – 1.5 gpm Low Flow Kitchen Faucet: 3.0 – 7.0 gpm Shower: 1.0 – 2.0 gpm Dishwasher: 1.0 – 2.5 gpm Clothes Washer: 1.5 – 3.0 gpm Tankless heaters are rated for how much heat they provide at a given flow. If ...


7

The typical way to pre-warm water is to install a standard tank water heater before the tankless, but leave it turned off. Using an automotive radiator is a terrible idea. You don't want to connect something not designed for potable water to your plumbing. That's just asking for trouble. The pex idea is interesting. The only reason that I can think that ...


6

With a tankless water heater it's all about how many degrees the heater can raise a certain quantity of water. In your situation, you will need a heater to raise the temperature of about 5 gallons per minute (two showers running at once or one shower and another hot water tap running). If you live in the north, and the water out of the tap is be 40 degrees ...


6

You could add a smaller tank-less heater in front. Some of them are even rated to be plugged into an outlet so you won't have to do additional electrical work. In Europe I've seen it done with a bigger unit to supply the whole house and a smaller one at the shower for use during the winter. In either case you're going to get a lot further with this ...


4

Do NOT use an automotive radiator - it's not meant for nor suitable for potable water use. If you have a "relatively warm basement" you can either use a plain, uninsulated pressure tank (a "tempering" tank in this application - cold in the bottom, warmed out the top) or run a long run of large-ish diameter PEX (to minimize pressure drop) around the basement ...


3

The manual will say something like Flushing the heat exchanger with a descaling solution if mineral build up is evident. Scale build up will shorten the life of the water heater, descale heat exchanger thoroughly and repeat annually depending on mineral content of ground water. (From Bosch 2400E NG user manual) or maybe something like Periodic ...


2

There are a few problems with your plan. Thermal Conductivity First off. If you're going to make a heat exchanger, you should use copper instead of PEX. Copper has a thermal conductivity of 401 watts/meter kelvin (W/mK), while PEX is closer to 0.51. Volume The next problem, is the volume of water you're preheating. 1" PEX has an inside diameter (I.D.) ...


1

Did you insulate your pipes beyond the water heater so that they are not losing the heat rise per foot? The hotter they stay before appliance the less demand for rise on the heater. Make sure you tape all the seams. Also do a tune on your heater -- often with both on boil and forced style heaters the efficiency and heat rise are below spec. I've seen ...


1

I'm not sure where you live but US code calls for a minimum of #8 if you're using copper or #6 if you're using aluminum. There would be no advantage in using a larger wire size in this case because at 30ft you will have negligible losses. I don't know what your voltage is or how many phases you have but for an example of what your losses may be, I will ...


1

In situations like this, I generally find that the manufacturer is a more reliable source of accurate information than an installer, especially an installer whom you are not using (but then again, you might be wise not to use them, too.) Some installers learned "a particular way" which is either outdated for current equipment or was simply wrong in the first ...


1

Tankless units are limited in the amount of hot water they can produce. It is rated at a certain number of gallons per minute. Think of it in terms of continuous versus multiple use. With a tankless unit rated at 7 gallons per minute you could shower with a 3 gallon per minute shower head until you ran out of fuel. If three people were multiple showering at ...


1

You're adding more points of failure, and when the small tank runs out, you will see a temperature drop until the tank fills with hot water from the reserve. You also have to worry about eventually reselling the home. Given that, my preference is to keep it simple with a single tank. One option to give you the same effect is a single electric tank with the ...



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